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Full text of "The Cambridge Natural History"

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THE animals that we considered in the last chapter, though show-
ing certain unmistakable likenesses to the mammals, are never-
theless unquestionably not mammals but reptiles. In the
Triassic strata, however, we first meet with the remains of
undoubted mammals. The Mammalia first appeared upon the
earth in a tentative and hesitating way: they had not cast off
many of the characters of their supposed reptilian forefathers;
they shrank from observation and destruction by their small size,
and apparently, so far at any rate as their teeth afford a clue, by
an omnivorous diet. The world abounded at that period in large
and carnivorous reptiles, which may indeed have been the
principal enemies with which the first mammals had to cope.
These early mammals lingered on to so late a period as the
Eocene; but the majority of the genera were Triassie, Jurassic,
and Cretaceous. Certain of the primitive mammalian forms have
been referred to the Marsupials, and their resemblances to the
Monotremata have also been pointed out. The current view of
the present time, however, is that they form a special order,
which may possibly have embraced the ancestors of both
Marsupials and Monotremes; for it is reasonable to explain in this
way the combination of characters of these two orders which they
present. For this group the name Allotheria has been proposed
by Marsh, and Multituberculata by Cope; the latter term is the
less suitable, in that the Monotremata (Ornithorhynchus) are also
" multituberculate." The group is known in a very imperfect
fashion. The remains are but few and fragmentary; and for the
most part we have only a few teeth to speculate upon. This is
natural enough, for the harder teeth might easily be supposed to